Cooling Circuit for Enhancing Turbine Performance

ABSTRACT

In a gas turbine having a compressor discharge casing, a cooling circuit diverts compressor discharge air toward a high pressure packing (HPP) circuit. The cooling circuit includes an inlet pipe that receives compressor discharge air. One or several cooled cooling air pipes are in fluid communication with the inlet pipe via a pipe manifold, which distributes the discharge air across the cooled cooling air pipes. A seal is disposed upstream of an entrance to the HPP circuit to limit flow into the HPP circuit, and a second seal is disposed downstream of the HPP circuit at turbine wheelspace to limit ingestion and thus the purge flow air required. The circuit serves to reduce required purge flow in the HPP circuit so that an amount of compressor discharge air can be put back to the main flow path, thereby improving turbine performance.

BACKGROUND OF THE INVENTION

The invention relates to a structure and method for enhancing turbineperformance and, more particularly, to a cooling circuit that divertscompressor discharge air to supplement the total required purge flow andcool critical turbine components.

The compressor discharge air leaking past the high pressure packing(HPP) of a gas turbine is typically returned to the primary gas path viathe first forward wheelspace, between the first stage nozzles and firststage buckets. This secondary flow path is referred to as the HPPcircuit. This air is used for two purposes: (1) it is used as purge flowin the first wheelspace to prevent hot gas ingestion; and (2) it coolscritical components in the HPP circuit. Some of the critical componentsin the HPP circuit include the compressor tie bolts, marriage joint,nozzle support ring and first stage wheel.

In some designs, the flow level in the HPP circuit is higher than thewheelspace purge requirement because of component temperaturerequirements. Therefore, an ideal solution should reduce the totalcircuit flow to a level that satisfies the wheelspace purge requirementswhile keeping all critical components in the circuit under desiredtemperature requirements. Furthermore, a preferred solution may also beable to handle robustly varying ambient and turbine operationconditions. Finally, the solution should be able to retrofit in theexisting hardware.

In a previous General Electric turbine design (the 9H turbine), an HPPcircuit utilized a cooled cooling air bypass system. The circuit used aheat exchanger to cool the extracted compressor discharge air and bringthe cooled cooling air to the front of the HPP circuit to not only coolthe last stages of the compressor components but also prevent a laterstage flow from coming into the HPP circuit. This system usesconventional sealing that the HPP and makes no attempt to regulate thepurge flow required beyond conventional angel wing seals. The cooledcooling air is not adjustable.

Brush seals have been implemented in other turbine designs to reduce thepurge flow. No cooled cooling air is needed there, however, because oflower compressor discharge temperatures and consequently lowertemperatures in the HPP circuit resulting in adequate wheelspacetemperature margins.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment, a cooling circuit in a gas turbine serves toaugment flow in a high pressure packing (HPP) circuit of the turbine.The cooling circuit includes an inlet pipe that receives compressordischarge air, and at least one cooled cooling air pipe in fluidcommunication with the inlet pipe via a pipe manifold. The pipe manifolddistributes the discharge air across the at least one cooled cooling airpipe. An upstream seal is disposed upstream of an entrance to the HPPcircuit, and a downstream seal is disposed downstream of the HPPcircuit.

In another exemplary embodiment, a method of improving turbineperformance using a cooling circuit by augmenting flow in a highpressure packing (HPP) circuit of the turbine includes the steps ofreceiving compressor discharge air in an inlet pipe; distributing thedischarge air across a plurality of cooled cooling air pipes; anddisposing an upstream seal upstream of an entrance to the HPP circuit toregulate air entering the HPP circuit and disposing a downstream sealdownstream of the HPP circuit to regulate a need for wheelspace purgeair.

In still another exemplary embodiment, the cooling circuit includes aninlet pipe that receives compressor discharge air; at least one cooledcooling air pipe in fluid communication with the inlet pipe via a pipemanifold, the pipe manifold distributing the discharge air across the atleast one cooled cooling air pipe; a cooling source in direct contactwith one of the at least one cooled cooling air pipe and the divertedair; a valve disposed between the inlet pipe and the at least one cooledcooling air pipe, the valve adjusting mass flow and a temperature of thediverted air based on a temperature of the HPP circuit; an upstream sealdisposed upstream of an entrance to the HPP circuit; and a downstreamseal disposed downstream of the HPP circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the cooling circuit of an exemplary embodiment; and

FIG. 2 shows the cooling circuit of an alternative exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, the system utilizes a seal 12 such as a brushseal, adjustable seal, or the like to prevent excessive flow from thecompressor discharge air and secondary (bypass) cooled cooling airsystem to supplement the total required purge flow and cool criticalcomponents. An adjustable seal can be one that is retracted duringengine transients to minimize wear or damage to the seal, or one thatallows for adjustment in service to accommodate seal performancedegradation.

The seal 12 is placed upstream or adjacent the HPP circuit entrancebefore all critical components and the existing honeycomb seal. Asnoted, the seal can be a conventional brush seal, an adjustable sealwith an actuating system, or the like.

An inlet tube or pipe 14 is positioned to receive compressor dischargeair. Preferably, the circuit includes two inlet tubes or pipes 14 ofabout 3″ diameter.

Diverted air in the inlet pipe 14 is flowed to a plurality of cooledcooling air pipes 16 via a pipe manifold 18. The pipe manifold 18distributes the discharge air from the inlet pipes 14 across the cooledcooling air pipes 16. The cooled cooling air pipes 16 direct thecompressor discharge air to the HPP circuit.

In a preferred arrangement, the cooling circuit includes 12 cooledcooling air pipes that penetrate at the compressor discharge casevertical flange and run along the compressor discharge case strut attrailing edges. The cooled cooling air pipes are preferably ¾″ or 1″ indiameter. The positioning via the compressor discharge case strutsserves to minimize the aerodynamic impact on the main gas flow. Acomputational fluid dynamics analysis has been conducted to ensure thatthe added tubing system has a negligible impact on the main gas flow.The tubes 16 further penetrate the compressor discharge casing innerbarrel flange via suitable apertures.

The circuit preferably additionally includes a cooling source incommunication with either or both of the inlet pipe 14 and the cooledcooling air pipes 16. In one arrangement, the cooling source comprisesambient air that serves to cool the air flow as it travels through thecooled cooling air pipes 16. Alternatively, the cooling source maycomprise a heat exchanger 20 such as a tube-shell type heat exchanger orthe like.

Still another alternative for the cooling source is an atomizer 22 thatsprays water droplets in contact with either the diverted air or thecooled cooling air pipes 16. The atomizer 22 preferably generatesmicro-level water droplets that are sprayed directly to cool theextracted air. The amount of water required to cool the flow by 150° F.will elevate the main gas path flow moisture level by only 2%. Locallyin the HPP circuit, the specific humidity will typically be 4-5 timescompared to the condition at the inlet. This higher humidity in generalis harmless to the circuit components.

FIG. 2 illustrates an alternative to the heat exchanger 20 or atomizer22 shown in FIG. 1. FIG. 2 illustrates an ejector 24 that mixes air fromthe 13^(th) stage of the compressor, or other suitable compressorextraction port, with the compressor discharge air. The 13^(th) stageair is directed to the ejector via suitable tubing 26 or the like. Thecombined 13^(th) stage and compressor discharge air at the ejector exitwill have a desired temperature and lower than the compressor dischargeair pressure. Because relatively cheaper air from stage 13, cheaper inthat less work has been done on the air to compress and heat it, isused, additional turbine performance can be gained.

The exit temperature and mass flow can be tuned by a valve 28 disposedbetween the inlet pipe 14 and the cooled cooling air pipes 16. Anadditional valve may be provided to control water mass when using theatomizer 22. The two valves can be operated either manually orautomatically by control signals. Preferably, the valves can beautomatically adjusted for desired mass flow and temperature of cooledcooling air based on a temperature measurement at the HPP circuit. Suchvalves can be used to regulate the CCA circuit regardless of the coolingmechanism used. These valves should be controlled based on temperaturemeasurements made in the HPP circuit; these are typically made atseveral locations in the wheelspace, but can also be made at anycritical location in the HPP circuit. Temperature measurements can beused to both determine that the cooling air is adequately cool, and toidentify the hot gas ingestion into the wheelspace.

The cooled cooling air pipes 16 deliver the cooling air at variouslocations relative to the HPP circuit. As shown in FIGS. 1 and 2,openings 30 are preferably provided in the inner barrel in order tosupply cooled cooling air to the tie bolt and marriage flange of theturbine. The remainder of the CCA is fed directly into the first forwardwheelspace.

The system and method described endeavor to save the amount ofcompressor discharge air required in the HPP circuit and redirect itback to the main flow path to enhance turbine performance. This can beachieved robustly by introducing a secondary flow system to bring cooledcooling air in the circuit. The amount of the total flow required in thecircuit is dictated by the wheelspace purge requirement. The differencebetween the wheelspace purge requirement and current flow is significantenough to justify the implementation of the secondary cooled cooling aircircuit. A seal limits the air entering the HPP circuit to the minimumpossible so that as much of the required purge air as possible issupplied by the cooled cooling air circuit. Improved sealing at thewheelspace via abradable angel wing seals reduces the amount of purgeair required. The mixed compressor discharge air and cooled cooling airshould be sufficient to prevent the wheelspace hot gas ingestion whilekeeping the critical components in the circuit under temperature limits.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A cooling circuit in a gas turbine for augmenting flow in a highpressure packing (HPP) circuit of the turbine, the cooling circuitcomprising: an inlet pipe that receives compressor discharge air; atleast one cooled cooling air pipe in fluid communication with the inletpipe via a pipe manifold, the pipe manifold distributing the dischargeair across the at least one cooled cooling air pipe; an upstream sealdisposed upstream of an entrance to the HPP circuit; and a downstreamseal disposed downstream of the HPP circuit.
 2. A cooling circuitaccording to claim 1, further comprising a cooling source incommunication with the at least one cooled cooling air pipe.
 3. Acooling circuit according to claim 2, wherein the cooling sourcecomprises ambient air.
 4. A cooling circuit according to claim 2,wherein the cooling source comprises a heat exchanger.
 5. A coolingcircuit according to claim 2, wherein the cooling source comprises anatomizer that sprays water droplets in contact with one of the divertedair and the at least one cooled cooling air pipe.
 6. A cooling circuitaccording to claim 2, wherein the cooling source comprises an ejectorthat mixes air from at least two compressor stages including thecompressor discharge.
 7. A cooling circuit according to claim 1, whereinthe cooled cooling air pipes penetrate a vertical flange of thecompressor discharge casing and extend along a compressor dischargecasing strut at trailing edges.
 8. A cooling circuit according to claim1, further comprising a valve disposed between the inlet pipe and thecooled cooling air pipes, the valve adjusting mass flow and atemperature of the diverted air based on a temperature of the HPPcircuit.
 9. A cooling circuit according to claim 1, further comprisingopenings in an inner barrel to permit cooled cooling air from the cooledcooling air pipes to reach at least one of a tie bolt and a marriageflange in the turbine.
 10. A cooling circuit according to claim 1,wherein the downstream seal comprises an abradable angel wing seal. 11.A method of improving turbine performance using a cooling circuit byaugmenting flow in a high pressure packing (HPP) circuit of the turbine,the method comprising: receiving compressor discharge air in an inletpipe; distributing the discharge air across a plurality of cooledcooling air pipes; and disposing an upstream seal upstream of anentrance to the HPP circuit to regulate air entering the HPP circuit anddisposing a downstream seal downstream of the HPP circuit to regulate aneed for wheelspace purge air.
 12. A method according to claim 11,further comprising actively cooling the cooled cooling air pipes.
 13. Amethod according to claim 12, wherein the actively cooling step ispracticed using ambient air.
 14. A method according to claim 12, whereinthe actively cooling step is practiced using a heat exchanger.
 15. Amethod according to claim 12, wherein the actively cooling step ispracticed using an atomizer that sprays water droplets in contact withone of the diverted air and the cooled cooling air pipes.
 16. A methodaccording to claim 12, wherein the actively cooling step is practicedusing an ejector that mixes air from at least two compressor stages. 17.A method according to claim 11, wherein the discharge air is regulatedby a valve.
 18. A cooling circuit in a gas turbine for augmenting flowin a high pressure packing (HPP) circuit of the turbine, the coolingcircuit comprising: an inlet pipe that receives compressor dischargeair; at least one cooled cooling air pipe in fluid communication withthe inlet pipe via a pipe manifold, the pipe manifold distributing thedischarge air across the at least one cooled cooling air pipe; a coolingsource in direct contact with one of the at least one cooled cooling airpipe and the diverted air; a valve disposed between the inlet pipe andthe at least one cooled cooling air pipe, the valve adjusting mass flowand a temperature of the diverted air based on a temperature of the HPPcircuit; an upstream seal disposed upstream of an entrance to the HPPcircuit; and a downstream seal disposed downstream of the HPP circuit.